Breast cancer is one of the most common types of cancer afflicting Western society. It is estimated that the spread of the disease has risen in the United States, from one in twenty women being afflicted in 1940, to one in eight in 1995. The American Cancer Society estimated that 183,000 new cases of breast cancer were reported during 1995. In the United States, some 46,000 women die from the disease per year. Today, it is accepted that the best way to detect breast cancer in its early stages is by annual mammography screening of women aged 40 and up.
The five-year survival rate for localized breast cancer is 93%. That rate drops to 72% if the cancer has spread regionally by the time of diagnosis. For patients with distant metastases at the time of diagnosis, the five-year survival rate is only 18%. Early diagnosis is thus of great importance to the cure. Since the interpretation of mammographic lesions is problematic, a need for advanced diagnostic tools is required.
The main mammographic findings that may indicate breast cancer are:                1. masses and densities        2. micro-calcifications        
The characteristics used to determine whether or not masses are malignant are: a) shape (regularity versus irregularity), b) margins (distinct or non-distinct), c) spiculation (thin lines extending from the mass).
The characteristics distinguishing between malignant or benign micro-calcifications are: size, form, pleomorphism within the cluster, cluster shape (if linear or branch-like), spatial density (if crowded or spread out) and relationship to masses.
Today, radiologists generally interpret the mammogram visually, using a light box, and their analysis is largely subjective. Film masking is used to highlight additional detail. In many cases, the radiologist employs supplementary tools such as a magnifying glass and bright light sources to evaluate very dark regions. If the mammogram is not conclusive the radiologist must recall the patient for an additional mammogram using one or more of the following techniques:                1. adding a view with a different projection.        2. performing a magnification mammogram by changing the distance between the breast and the film.        3. locally compressing the breast in the area of suspected abnormality.The analysis, even after using the above techniques, still remains mainly subjective.        
All the statistical data related to the conventional mammogram process were published in scientific literature and concern the U.S. population only. It is assumed that these data are also relevant outside the U.S.                1. Most professional organizations recommend that women over age 40 have a mammography examination once a year.        2. There is a recall rate of about 20%. This is the percentage of patients recalled to perform further examinations, essentially another mammogram.        3. About 3% of women who are evaluated by screening mammography are referred for a biopsy.        4. In screening mammography, about 60 malignancies are found in a sample of 10,000 cases.        5. The false negative rate of the mammographic screening process is difficult to estimate. It is generally accepted that 15% of the women who have ultimately been diagnosed with breast cancer and who had a mammogram performed during the previous 12 months were not originally diagnosed with cancer.        6. The false positive rate of the screening mammography process, i.e. the rate of negative results of biopsies performed due to the screening process, is about 80%.        
In order to aid radiologists in reducing the false negative rate in mammographic screening, computer systems using specialized software and/or specialized hardware have been developed. These systems, often called computer-aided detection systems, have been known for many years and have been reported extensively. As noted below, their use in evaluating mammograms has been discussed at length in both the patent and professional literature.
Reading large numbers of mammograms is a difficult and tiring task. According to some literature reports as noted above, unacceptably high rates of false negative results occur. Using computer-aided detection systems provides an independent detection mechanism assisting radiologists in attaining higher malignancy detection rates, i.e. reducing false negative rates.
However, it is well known that computer-aided detection systems almost invariably indicate more suspected abnormalities than are detected by a trained radiologist. The number indicated is often significantly greater than can easily be reviewed. Therefore, a radiologist may have to examine, and must often dismiss, not only the suspected abnormalities that he detects from the radiological mammogram films but also the additional, typically greater number of, suspected abnormalities detected by the computer-aided detection system. Depending on how many more additional suspected abnormalities the computer-aided detection system detects and identifies on the display, the extra work in examining and dismissing these additional abnormalities can slow down the diagnostic process. Even with the use of confidence levels, which usually are insufficiently detailed and nuanced, the task of reviewing the many false locator markers displayed by the system may be more tiresome and troublesome than the benefits that accrue from looking more carefully into the individual suspected lesions.
Computer-aided detection and computer-aided diagnosis (CAD) mammography systems have been discussed extensively in many issued patents. An overview of the field can be obtained by reviewing U.S. Pat. No. 5,729,620 (Wang); U.S. Pat. No. 5,815,591 (Roehrig, et al); U.S. Pat. No. 5,828,774 (Wang); U.S. Pat. No. 5,854,851 (Bamberger, et al); U.S. Pat. No. 5,970,164 (Bamberger, et al); U.S. Pat. No. 6,075,879 (Roehrig, et al); U.S. Pat. No. 6,198,838 (Roehrig, et al); U.S. Pat. No. 6,266,435 (Wang); and U.S. Pat. No. 6,434,262 (Wang). These patents, including references cited therein, are hereby incorporated by reference in this specification as though fully set forth herein.